Stand composition and structure as indicators of epixylic diversity in old-growth boreal forests

Abstract

This study aims to evaluate the relative contribution to biodiversity of 4 dominant types of virgin black spruce (Picea mariana) forests found in a typical regional landscape of the black spruce-moss bioclimatic domain of central Québec: mature black spruce forests with a regular structure, old black spruce forests with a regular structure, old black spruce-fir (Abies balsamea) mixed forests with 2 stories, and mixed forests with irregular structure. A total of 16 stands covering these 4 forest types were sampled to characterize forest composition and structure as well as epixylic communities. Multivariate analyses of variance were performed to evaluate to what extent the epixylic community structure differed among the 4 forest types. Results show that the old two-story and irregular forest types sustain higher species richness of epixylics per unit area; therefore, these types may be key habitats for old-growth dependent species of bryophytes and lichens. The close association of epixylics with these forest types was mainly due to better moisture conditions and the presence of greater amounts of coarse woody debris in advanced decaying stages. We also demonstrated that forest compositional and structural attributes are good indicators of epixylic diversity. Finally, we suggest that maintaining old irregular black spruce-fir mixed forests should be the primary aim of conservation strategies for old-growth forests.